1. Field of the Invention
This invention concerns a process for feeding additives into a polymer melt stream, wherein a substream is taken from the polymer melt stream, mixed with additives, and thereafter supplied into the polymer melt stream again.
2. Summary of the Related Art
Feeding additives into a polymer melt stream is know. A process for feeding additives into a polymer melt stream is described in Chemiefasern/Textilindustrie [Manmade Fibers/Textile Industry], vol. 36/88, January 1986, pages 24 to 29, with a substream of approximately 5% to 10% being removed from an unmodified main melt stream discharged from a final reactor or extruder and sent through a twin screw extruder equipped with special kneading elements. Suitable additives are added to the twin-screw extruder with a continuous metering system and incorporated homogeneously into the melt. Then the melt loaded with additives is mixed back into the main melt stream, with a uniform distribution of additives being achieved by means of static mixing elements.
German Patent No. 4,039,857 describes a process and a device for direct continuous modification of polymer melts. A substream of melt, to be optionally modified, is taken from the main stream of melt and sent into a twin screw extruder. The additives pass through a delivery pump into the twin screw extruder. The modified melt substream is then sent back to the main melt stream.
European Patent No. 532,988 describes a process for producing random copolyesters. According to a preferred embodiment, a polyester (B) and 10 to 50 wt % of a polyester (A) are sent to a mixing extruder, and the extrudate is then mixed with the remaining 90 to 50 wt % of polyester (A) in a static mixer.
It is known from Franz Fourne, Synthetische Fasern [Synthetic Fibers], Hanser Verlag, 1995, pages 316 through 318, that planet wheel spinning pumps can be used to convey polymer melts. These planet wheel pumps usually have three to eight pump gear wheels arranged in one plane about a planet gear wheel that serves as the drive. The only melt inlet is in the form of a flow channel in the middle, and each of the n outlets is arranged in one gear wheel wedge.